1. Field of the Invention
This invention relates to an electrophotographic photosensitive member, and more particularly to an electrophotographic photosensitive member having a surface layer containing a resin with a specific structure. This invention also relates to an electrophotographic apparatus and an apparatus unit which have such an electrophotographic photosensitive member.
2. Related Background Art
Inorganic materials such as selenium, cadmium sulfide and zinc oxide are hitherto known as photoconductive materials used in electrophotographic photosensitive members. Organic materials including polyvinyl carbazole, phthalocyanine and azo pigments have attracted notice on the advantages that they promise a high productivity and and freedom from environmental pollution, and have been put into wide use although they tend to be inferior to the inorganic materials in respect of photoconductive performance or running performance. In recent years new materials having overcome such disadvantages have been studied, and are surpassing the inorganic materials particularly with regard to photoconductive performance.
Meanwhile, electrophotographic photosensitive members are required to have durabilities to various external forces of physical, chemical and electrical origins since they are repeatedly affected by charging, exposure, development, transfer, cleaning and charge elimination in electrophotographic processes in copying machines or laser beam printers. In particular, mechanical strength such as wear resistance or scratch resistance is one of important factors for determining the running lifetime of electrophotographic photosensitive members. Since the organic photoconductive materials have no film-forming properties by themselves, it is common for them to be formed into films with use of binders when photosensitive layers are formed. Thus, the properties of binder resins can be a factor that greatly influences the mechanical strength. Accordingly, it has been attempted to make binder resins having a higher molecular weight, to use curable resins and also to use lubricants such as Teflon.
However, the use of high-molecular weight binder resins is problematic in that it causes an increase in viscosity of layer forming coating materials. The use of curable resins may cause a deterioration of organic photoconductive materials when cured, and a deterioration of electrophotographic performance that is ascribable to the presence of unreacted functional groups or impurities such as polymerization initiators. Also, the use of lubricants cannot be well satisfactory in view of film forming properties and compatibility.
As image quality and durability have been made much higher in recent years, studies have been made on electrophotographic photosensitive members that can stably provide better images over a long period of time.